Generally, integrated circuits (ICs) comprise electronic components, such as transistors, capacitors, or the like, formed on a substrate. One or more metal layers are then formed over the electronic components to provide electrical connections between the electronic components and to provide electrical connections to external devices.
The trend in the semiconductor industry is towards the miniaturization or scaling of integrated circuits, in order to provide smaller ICs and improve performance, such as increased speed and decreased power consumption. While aluminum and aluminum alloys were most frequently used in the past for the material of conductive lines in integrated circuits, the current trend towards IC miniaturization necessitates the use of copper for a conductive material because copper has lower activation energy than aluminum, allows higher current densities than aluminum, better electrical characteristics than aluminum, and has higher thermal conductivity than aluminum, as well as decreased resistance and a higher melting point.
The change from aluminum to copper conductive lines has introduced new challenges in the manufacturing process. For example, copper surfaces oxidize easily when exposed to oxygen. This may present bonding issues for copper surfaces which are exposed to air.